1. Field of the Invention
The present invention relates to an air-conditioner for use in an automotive vehicle, the air-conditioner having a heater for heating air to be supplied to a passenger compartment, the heater being powered by heat sources, such as electricity, other than waste heat of an internal combustion engine. The air-conditioner is suitably used in an electric vehicle powered by a fuel cell or in a so-called hybrid vehicle powered by a combination of an internal combustion engine and an electric battery.
2. Description of Related Art
A conventional air-conditioner mounted on a vehicle powered by an internal combustion engine includes a heater utilizing waste heat of the engine and a refrigeration circuit driven by the engine. Air introduced into the air-conditioner is first cooled by an evaporator of the refrigeration circuit. Part of the cooled air is led to the heater to reheat the cooled air, and the other part of the cooled air is directly supplied to a passenger compartment, bypassing the heater. An amount of the cooled air bypassing the heater is controlled by an air-mixing door to thereby control temperature of the air supplied to the passenger compartment.
In the air-conditioner for the electric vehicle or the hybrid vehicle, it is impossible or difficult to utilize the waste heat from the engine for the heater. Therefore, an electric heater or a combustion heater is used in such an air-conditioner. If the temperature of the air supplied to the passenger compartment is controlled in the same manner as in the conventional air-conditioner, i.e., by mixing the cooled air and the heated air, a large amount of electric power is required for heating and for operating the refrigeration cycle.
In order to cope with this problem, a proto-type air-conditioner that is selectively operable under three modes is made and tested. The three modes are: a cooling mode in which the temperature of the air supplied to the passenger compartment is solely controlled by adjusting a cooling ability of an evaporator in a refrigeration circuit; a heating mode in which the air temperature is solely controlled by adjusting a heating ability of the heater; and an air-mixing mode in which the air temperature is controlled by mixing the cooled air and the heated air.
Following problems have been found in the proto-type air-conditioner. That is, when the operating mode is switched from the heating mode or the air-mixing mode to the cooling mode, the temperature of the air supplied to the passenger compartment is abruptly changed to a lower temperature. This is because the heated air flowing through the heater abruptly disappears upon switching the operation mode to the cooling mode. This makes passengers uncomfortable. Similar problems are found when the operating mode is switched from the cooling mode or the air-mixing mode to the heating mode. The temperature of the air supplied to the passenger compartment is abruptly changed to a higher temperature upon switching the mode to the heating mode, because the cooled air flowing through the evaporator abruptly disappears. This is detrimental to comfort of the passengers.